Sound recording



(UNITED STATES- PATENT oia SOUND nnoonnnvo 4 William L Woolf, Long Island, N. Y., assignor to Film Recording Corporation, a. corporation-f New York Application May 15, 1936, Serial No. 80,010

2 Claims. c1. 274-38) This invention relates to a method of producing is even less due to this flowing action of t a sound record on any suitable substance, usually terial. The large diameter of an embossing plastics or metals, such as wax, phenolic resins, needle also attenuates high frequencies because cellulose acetate, cellulose nitrate, and other celthe needle destroys its own record when thedi- 5 lulose compounds, aluminum, zinc, silver or'gold, ameter of the needle is not very small compared 5 whether the substance be in-the form of a cylinwith the distance traversed by the film during the der, disc or strip. recording of a full wave.

. More particularly it relates to recording sound I have found after, extensive experimentation impulses on a strip of film. The sound record that I can, by properly shapingthe point of the may be made on the film in synchronism with a cutting stylus, obtain the highfrequencies inher- 10 motion picture, or it may be made on the film ent in the sharp cutting needle, and the freedom without a picture or without any light sensitive from needle scratch associated with the burnishemulsion as the emulsion plays no useful part ing needle. The shape of the cutting stylus will in recording sound in accordance with my invenbe most readily understood by assuming that I tion. One object of this invention, is to produce a form it first as a cone with a hemispherical ter- 15 7 long time playing record in small, compact and minus, approximately twothousandths of aninch convenient form. Another object is to produce a in diameter and that I then grind away slightly long time playing record at a low cost through less than the front half of this needle, leaving a permitting it'to be widely used for many purplain surface as the front face; This needle has poses, such as recording speeches, proceedings of sharp cutting edges and cuts away a portion of 29 conventions, meetings, court records, radio prothe material of .the record. The rounded rear grams, telephone conversations, executive orders, P ti of he n ed e bu s the P m d legal documents, letters, dictation, etc. by cutting and leaves it smooth and compara- I am fully aware that numerous attempts have tively free from needle scratch. The shape of been made to produce a satisfactory sound record t s needle is sh w y t aeeempahying ewon a ribbon, strip, or motion picture film. Some in have tried recording with aheated stylus; Others y invention is illustrated in t e accompany?- have tried various means which soften or tend to s drawing n ch: soften the material of the strip for recording pur- Figure 1 is an enlarged fra y VieW'shOW- 30 poses, som have t i d recording ith sharp v ing the, lower end of the needle in front elevation 30 shaped stylus which cuts into the material and and in enga h t fi s own in secremoves a thin thread from the record groove. tiOn;

This method leaves the groove so rough that Figure 2 is enlarged View like re 1 butwhen the sound is reproduced the scratch level showing the ne dle n si ele and is unduly high. Inorder to overcome the scratch ur 3 shows a short length of P e fi m level, burnishing has been tried. This isthe most with three sound grooves recorded in the usual successful method-at the present time. By this sound track ereamethod a conical shaped stylus is employed which Fi u 4 s sections-1 View taken along line terminates ina hemispherical shaped extremity. 4-4 of Figure 40 The rounded needle forces the material down and u e 1 is a front View Of e P i O the 40 out, and compresses it, leaving the material of needle' eatly amplified engaging afilm C. The the groove imbedded in the film. This method line 3-3 is the contour of the needle while the polishes the groove and greatly diminishes the e AA ep ese ts e e fl ehe l ne needle-scratch. This method has inherent in it, 3-3 represents the plane of widest dimension of however, two disadvantages; both of which tend the needle, thatis, a. plane coinciding with the 45 to attenuate the recordingof'the high frequencies. axis of the needle. "The axis of the-needle is First, is the comparatively heavy pressure reshown by the line. D in Figures 1 and 2. The quired on the needle, and second is the comperafront surface or cutting faceQF of the stylus may tively large diameter of the needle, particularly be flat, concave or slightly convex. The plane the diameter parallel to the recording groove. I passingthrough; the linen-A and bounded The high pressure and large diameter tend to thereby is similar in shape, parallel to and cause the material of the record to flowwith a slightly smaller than the plane passing through jelly-like motion so that on the high frequencies and bounded by the line 3-3. The cutting edge wherein the amplitude of vibration of the needle A-A of the cutting face CF cuts away a portion i ve y e the amplitudeinthe recorded groove of the material of the groove. The rounded por- Figure 2 shows a side view. of the needle greatly amplified. The thickness of the needle from front to back is approximately one-half that of the rounded needle, and the pressure on this type of needle can be very considerably less than that applied to rounded needles. Furthermore, the lateral movement of the needle during recording is accomplished with less pressure than that required with a round needle thus diminishing the flowing action of the record material. As indicated above, I prefer to form'the point of the needle as a cone having a hemispherical or rounded terminus approximately two-thousandths of an inch in diameter. The front or cutting face of the needle is formed by grinding away slightly less than the front half of the cone, leaving a plane surface CF as a front or cutting face, as shown in Figure 2. The boundary of the cutting face is indicated by the line A-A in Figure 1. The curved surface located between the cutting face CF (plane AA) and the central transverse plane BB forms a burnishing surface bounding all parts of the edge of the cutting face CF. The separation between the cutting face CF and the central transverse plane 3-3 in Figure 4 has been exaggerated over the showing in Figure 2 for the purpose of more clearly showing the curvature of the burnishing surface. The distance between the two planes A-A and B-B will depend upon seyeral factors including the character of the material of the sound record and also on the degree 'of burnishing desired. The greater the separation between these two planes, the greater will be the burnishing and vice versa. Accordingly, where it is desired to decrease the needle scratch, the distance between the two planes will be increased, but where it is desired to emphasize the high frequencies, this distance will be decreased. The included angle of the conical point will also depend upon several factors which may be easily determined, such as the weight carried by the needle and the hardness of the material of the record. The cutting angle, that is, theangle which the axis of the needle bears to the surface of the record will also vary somewhat with difi'erent conditions, but in general it will be slightly inclined away from the right angular position as shown in Figure 2. The cutting point is preferably made of diamond, although needles made of sapphire or steel may be employed.

Figure 3 represents a sample piece of motion picture film showing three sound grooves E in the space usually occupied by one sound track. As explained above, the separate sound grooves may represent three voice records all in different languages, or they may be identical sound recordings so that in the event of excessive wear in one groove, the other grooves may be used. I have also indicated above that for long-time playing records, the entire area of the film between the sprocket holes may be used for recording. and in order to have the film move continuously in one direction, it may be formed as an endless belt, or if .desired, alternate sound grooves may be recorded and reproduced by running the film in opposite directions.

Having described my invention, what I desire to secure by Letters Patent is:

l. A recording stylus having a point conforming in shape to the larger part of a cone of rounded apex which has been out along a plane parallel to and spaced from its longitudinal axis, whereby burnishing surfaces are provided surrounding the cutting face of the stylus.

2. A sound recording stylus. having a point formed of a substantially conical body portion having a substantially fiat cutting face formed thereon substantially parallel to the axis of said conical body, said cutting face being displaced forward of said axis to provide burnishing surfaces bordering the sides of said. cutting face, and said body portion being rounded at the terminus thereof.

WILLIAM L. WOOLF'. 

